Rotation of cycloalkanes

[rebecca_handler_1B]

I understand that cyclopropane does not rotate and cyclobutane does, but I don't understand why that is. Can someone help me understand this?

[Marco_Romo_1M]

Looking at the 3-D model of cyclopropane, there is no conformation that could result in the 3 carbon molecules to not be in the same plane. For cyclobutane, two of the carbons can go up or down together, creating a non planar formation (butterfly) which is more stable because there is less torsional strain.

[Shelby Slaughter 3D]

The Carbon atoms in cyclobutane, unlike cyclopropane, can rotate to stagger the hydrogen atoms and relieve torsional strain. Cyclopropane must be planar, and cyclobutane takes a butterfly confirmation because it is more stable this way than as planar.